'\" te
.\" Copyright (c) 2008, Sun Microsystems, Inc., All Rights Reserved
.\" The contents of this file are subject to the terms of the Common Development and Distribution License (the "License").  You may not use this file except in compliance with the License.
.\" You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE or http://www.opensolaris.org/os/licensing.  See the License for the specific language governing permissions and limitations under the License.
.\" When distributing Covered Code, include this CDDL HEADER in each file and include the License file at usr/src/OPENSOLARIS.LICENSE.  If applicable, add the following below this CDDL HEADER, with the fields enclosed by brackets "[]" replaced with your own identifying information: Portions Copyright [yyyy] [name of copyright owner]
.TH DDI_MODOPEN 9F "Mar 17, 2008"
.SH NAME
ddi_modopen, ddi_modsym, ddi_modclose \- dynamically-loaded kernel module
functions
.SH SYNOPSIS
.nf
#include <sys/modctl.h>

\fBddi_modhandle_t\fR \fBddi_modopen\fR(\fBconst char\fR\fI*modname\fR, \fBint\fR \fImode\fR,
     \fBint\fR \fI*errnop\fR);
.fi

.LP
.nf
\fBvoid\fR \fB*ddi_modsym\fR(\fBddi_modhandle_t\fR \fIhandle\fR, \fBconst char\fR \fI*symname\fR,
     \fBint\fR \fI*errnop\fR);
.fi

.LP
.nf
\fBint\fR \fBddi_modclose\fR(\fBddi_modhandle_t\fR \fIhandle\fR);
.fi

.SH INTERFACE LEVEL
illumos DDI specific (illumos DDI).
.SH PARAMETERS
.ne 2
.na
\fB\fImodname\fR\fR
.ad
.RS 11n
The name of the dynamically-loaded kernel module (file) to be opened. The
\fImodname\fR string is of the form:
.sp
.in +2
.nf
"[\fInamespace\fR/[\fIdirspace\fR/]]\fImodulename\fR"
.fi
.in -2
.sp

Each "\fInamespace\fR/" directory along the standard kernel
moddir/\fImodule-path\fR path (\fBsystem\fR(5)) is searched to locate the
module. If "\fInamespace\fR/" is not specified, "misc/" is assumed. If
"\fIdirspace\fR" is specified, then "\fInamespace\fR/" must be explicitly
provided.
.RE

.sp
.ne 2
.na
\fB\fImode\fR\fR
.ad
.RS 11n
Currently, \fBKRTLD_MODE_FIRST\fR.
.RE

.sp
.ne 2
.na
\fB\fIerrnop\fR\fR
.ad
.RS 11n
Pointer to \fBerrno\fR returned on error, if \fBNULL\fR then no additional
error information is available.
.RE

.sp
.ne 2
.na
\fB\fIhandle\fR\fR
.ad
.RS 11n
Opaque handle returned from \fBddi_modopen()\fR, invalidated by
\fBddi_modclose()\fR.
.RE

.sp
.ne 2
.na
\fB\fIsymname\fR\fR
.ad
.RS 11n
Symbol's name as a character string.
.RE

.SH DESCRIPTION
The function prototypes for \fBddi_modopen()\fR, \fBddi_modsym()\fR, and
\fBddi_modclose()\fR are modeled after the userland \fBlibdl\fR(3LIB),
\fBdlopen\fR(3C), \fBdlsym\fR(3C), and \fBdlclose\fR(3C) interfaces, however
not all userland features are available and the kernel symbol resolution is
different. The \fBdlerror\fR(3C) interface is not appropriate for the kernel
environment, so the new \fIerrnop\fR return argument was added for
\fBddi_modopen()\fR and \fBddi_modsym()\fR.
.sp
.LP
The \fBddi_modopen()\fRfunction makes a dynamically-loaded kernel module named
by "modname" available to a running kernel. \fBddi_modopen()\fR returns a
handle that the caller can use on subsequent calls to \fBddi_modsym()\fR and
\fBddi_modclose()\fR. The value of this handle should not be interpreted in any
way by the caller.
.sp
.LP
The \fBddi_modopen()\fR interface works best as a dynamic component/object
plug-in mechanism when targeting kernel "misc" modules that contain a single
"struct modlmisc" module linkage, however non-"misc" modules and modules with
multiple linkage structures can also be targeted.
.sp
.LP
There are two different symbol resolution search orders associated with the
\fBddi_modopen()\fR function: one search order to resolve symbols during the
load of the targeted module, another search order o resolve \fBddi_modsym()\fR
calls against the handle returned by \fBddi_modopen()\fR. To resolve symbols
during module load, the standard kernel module load search order is used; to
resolve symbols during module "A" load, the order is as follows:
.sp
.in +2
.nf
A -> A's _depends_on -> unix -> unix's _depends_on
.fi
.in -2
.sp

.sp
.LP
A single-level, left-to-right search in \fB_depends_on\fR (or the "ld -N"
alternative) modules occurs. For \fBUNIX\fR on \fBSparc\fR, \fB_depends_on\fR
is similar to "genunix misc/platmod cpu/SUNW,UltraSPARC-III+  dtracestubs" for
\fBIntel\fR, it is "genunix dtracestubs". The \fBddi_modsym()\fR search is
limited to the module directly associated with the handle.
.sp
.LP
The \fBddi_modopen()\fR function increments the reference count on the named
kernel module. Upon the first load of a module, the \fB_init\fR(9E)
initialization code in the module is called; \fBddi_modopen()\fR does not
return until \fB_init\fR completes.
.sp
.LP
The \fBddi_modsym()\fR function allows a caller to obtain the address of a
symbol that is defined within a module. The \fIhandle\fR argument is a valid
\fBddi_modhandle_t\fR as returned by \fBddi_modopen()\fR, the \fIsymname\fR
argument is the symbol's name as a character string. The special handle values
supported by ddi_modsym(9F) are not supported.
.sp
.LP
The \fBddi_modclose()\fR function decrements the reference count of the kernel
module associated with the specified handle. After the \fBddi_modclose()\fR
function is called, all \fBddi_modsym()\fR resolutions obtained (either
directly or indirectly) using the now closed \fIhandle\fR are invalid; further
use of these resolutions can cause undefined behavior (that is, may lead to a
panic). When the last \fBddi_modclose()\fR of a module occurs, and there are no
further references to the module, the module \fB_fini\fR(9E)entry point may be
called. If \fB_fini\fR returns success then the module may be unloaded.
.SH RETURN VALUES
The \fBddi_modopen()\fR function returns a handle to the dynamically-loaded
kernel module. The \fBddi_modopen()\fR function returns \fBNULL\fR if the
module cannot be found, the object cannot be relocated, or an error occurs
during the process of resolving and relocating its symbolic references.
.sp
.LP
The \fBddi_modsym()\fR function returns \fBNULL\fR if the \fIsymname\fR symbol
cannot be found directly within the module associated with the \fIhandle\fR.
.sp
.LP
If the \fIhandle\fR was not referenced, \fBddi_modclose()\fR returns 0. If the
\fIhandle\fR is invalid, \fBddi_modclose()\fR may return a non-zero value.
.sp
.LP
When either \fBddi_modopen()\fR or \fBddi_modsym()\fR return \fBNULL\fR,
additional \fIerrno\fR information related to the failure is returned in
\fI*errnop\fR if it is not \fBNULL\fR.
.SH CONTEXT
\fBddi_modopen()\fR can be called from user context only.
.SH EXAMPLES
\fBExample 1 \fRCoding a Dynamically Loaded Kernel Module
.sp
.LP
The following example shows code to dynamically load and call a "\fBtest\fR"
interface in a module called "\fBdltest\fR". The "\fBtest\fR" interface  then
adds one to its integer argument.

.sp
.in +2
.nf
ddi_modhandle_t modh;
int             (*test)(int);
int             i = 0;
int             errno;
---%<---
/* dynamically load "dltest" kernel 'misc' module */
modh = ddi_modopen("dltest", KRTLD_MODE_FIRST, &errno);
if (modh == NULL)
         goto fail;      /* failed to open dltest module */

test = (int (*)())ddi_modsym(modh, "test", &errno);
if (test == NULL) {
        (void) ddi_modclose(modh);
        goto fail;      /* failed to find "test" interface */
}

/* invoke test interface and verify result */
i = (*test)(0);
ASSERT(i == 1);

(void) ddi_modclose(modh);
---%<---
.fi
.in -2

.sp
.LP
The implementation of the "dltest" "misc" module is as follows:

.sp
.in +2
.nf
#include <sys/modctl.h>
static dltest_add = 0;

/* define the module linkage */
static struct modlmisc          modlmisc = {&mod_miscops, "dltest"};
static struct modlinkage        modlinkage = {
        MODREV_1, (void *)&modmisc, NULL
};
int
_init(void)
{
        int     i;

        dltest_add = 1;                 /* initialization */
        if ((i = mod_install(&modlinkage)) != 0)
                dltest_add = -1;        /* un-initialization */
        return (i);
}
int
_fini()
{
        int     i;

        if ((i = mod_remove(&modlinkage)) == 0)
                        dltest_add = -1;        /* un-initialization */
        return (i);
}
int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}

/* "test" interface */
int
test(int i)
{
        return (i + dltest_add);
}
.fi
.in -2

.LP
\fBExample 2 \fRDynamically Accessing a Kernel Module within a Drive
.sp
.LP
The following example shows driver code to dynamically load into the kernel a
module constructed via the \fBelfwrap\fR(1) utility and containing firmware
intended for download to a device. The "\fBstart\fR" and "\fBend\fR" pointers
provide the addresses of the beginning of the data and first byte beyond the
data.

.sp
.in +2
.nf
ddi_modhandle_t modp;
char *data_startp, *data_endp;
size_t nbytes;
int rv;

modp = ddi_modopen("firmware-rev1.2a", KRTLD_MODE_FIRST, &rv);
data_startp = (char *)ddi_modsym(modp, "fw-rev1.2a_start", &rv);
data_endp = (char *)ddi_modsym(modp, "fw-rev1.2a_end", &rv);
nbytes = data_endp - data_startp;
rv = ddi_modclose(modp);
.fi
.in -2

.SH SEE ALSO
.BR elfwrap (1),
.BR dlclose (3C),
.BR dlopen (3C),
.BR dlsym (3C),
.BR libdl (3LIB),
.BR system (5),
.BR boot (8),
.BR modload (8),
.BR _fini (9E),
.BR _info (9E),
.BR _init (9E)
.sp
.LP
\fIWriting Device Drivers\fR
.SH WARNINGS
A \fBsystem\fR(5)forceload must be established for modules targeted by
\fBddi_modopen()\fR by code involved in the mount of root on "bootdev" during
machine \fBboot\fR(8).
